This invention relates to use of polymeric films in sensors.
Mass-sensitive sensors have varying configurations. Typically, a sensor is provided with a chemically sensitive film that is applied onto a surface of the sensor, for example onto the surface of the sensor""s crystal. Interactions of the film with a material to be detected, for example an analyte, induce a change in at least one of the mass and visco-elastic properties of the film. This change is measured as a shift of the resonance frequency of the sensor""s crystal and is related to the concentration of the analyte. For detection of analytes of differing nature, the coating and analyte interactions include, but are not limited to, hydrogen bonding, xcfx80-stacking, acid-base, electrostatic and size/shape recognition.
The sensor""s configuration, materials, and other characteristics vary to define operational characteristics, resonance frequencies, and boundaries for the sensor. For example, differing piezoelectric materials for a sensor substrate operate differently, and thus define the sensor""s operational boundaries and characteristics. Therefore, if a sensor comprises a quartz crystal microbalance (QCM) as a sensor substrate, the sensor operates by propagating mechanical oscillations generally perpendicularly between parallel faces of a thin, quartz-crystal piezoelectric element. If a sensor comprises a surface acoustic wave (SAW) device as a sensor substrate, mechanical oscillations are propagated in substantially up-and-down undulations at a radio frequency (RF) along the surface of a thin, quartz-crystal piezoelectric element.
The chemically sensitive film permits the sensor to more readily detect a target analyte or other compound (hereinafter xe2x80x9ctarget compoundxe2x80x9d), which is not ordinarily sensed by the sensor. The sensitive film often comprises a polymeric material film (hereinafter xe2x80x9cpolymeric filmxe2x80x9d), which changes the response of the sensor by altering the sensor""s mechanical oscillation frequencies, and thus permitting the target compound to be detected by the sensor. The sensor""s changing frequencies result from the polymeric film""s interaction with the target compound. Accordingly, various target compounds can be detected by a sensor when the nature of reaction between the polymeric film and target compound is known.
The target compound, usually a vapor, is dissolved (absorbed) into the film, by a process known in the art as xe2x80x9cpartitioning.xe2x80x9d A partition coefficient, K, is a thermodynamic parameter that corresponds to an equilibrium distribution of sorbed molecules between the gas phase and polymeric film. The partition coefficient is ratio of a concentration of target compound in the polymeric film, CF, to the concentration of the target compound outside of the film, CV. The partition coefficient K is determined according to Equation (1)
K=CF/CVxe2x80x83xe2x80x83(Equation 1)
One example of such an altered frequency results from a changed polymeric film mass. An increased film mass lowers a frequency at which the crystal oscillates, including for which it oscillates when exposed to a target compound. Thus, the target compound perturbs the oscillation of the sensor when the mass of the polymeric film increases, and thus the target compound can be detected. The oscillation frequency and mass change of a polymeric film often necessitate that it be thin and mechanically rigid. The thin nature of a polymeric film is needed so that the polymeric film""s visco-elastic properties, and any changes in those visco-elastic properties produced by partitioning of the target compound thereto, do not adversely influence the oscillations of the sensor and provide inaccurate detection of a target compound. Further, the polymeric film should be mechanically rigid so the sensor provided with the polymeric film can have repeated sensing applications.
SAW sensor devices coated with thin polymeric material film (known in the art as xe2x80x9cchemosensorsxe2x80x9d) have been used as micro-sensors for detecting vapors. The sensitivity to a specific vapor (target compound) for such a SAW chemosensor depends on the type, physical and chemical properties, and materials of polymeric film. For example, each of a polymer-vapor partition coefficient, rate of absorption, and desorption processes influence the operational characteristics of a polymeric film. Examples of materials for polymeric films used as on a SAW chemosensor include, but are not limited to, phenyl-methyl-polysiloxanes, poly(epichlorohydrin), poly(isobutylene), poly(ethylene maleate), and poly(ethylenimine). Some of these materials do not provide stable operations in which controlled, accurate, reliable, and repeated detections are possible. Although SAW sensors are more sensitive than QCM sensors, the relatively low partition coefficients of polymers used in the past preclude the use of SAW and QCM sensors for detection of low concentrations of analytes.
A sensor with polymeric film that provides capabilities for determination of low concentrations of analytes (also known as target compounds) is needed. The polymeric film should also provide a long term stability of operation for reliable detection results.
A sensor comprises a substrate and a polymeric film disposed on the substrate. The polymeric film comprises at least one hardblock component and at least one softblock component.
The invention also sets forth a method for enhancing detection of a target compound by a sensor. The method comprises disposing a polymeric film on a surface of the sensor, in which the polymeric film enhances detection of target compounds not normally sensed by a sensor without the polymeric film. The polymeric film comprises at least one hardblock component and at least one softblock component.
A polymeric film for a sensor is further set forth by the invention. The polymeric film comprises at least one hardblock component and at least one softblock component.
These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.